Process for hardening steel alloys



Patented Mar. 18, 1924.

ADOLF FRY, ESSEN-STADTWALD, GERMANY, ASSIGNOR TO FBTED. KRUPP .AK'LIEN-GISELLSCEAIT, OF ISSEN-ON-THE-RUHR, 1" H PROCESS FOR HARDENING STEELALLOW.

No Drawing.

To all whom it may concern:

Be it known that I Anonr FRY, residing at Essen-Stadtwald, Germany, acitizen of the German Republic, haveinvented a certain new and usefulImprovement in Processes for Hardening Steel Alloys, of which thefollowing is a specification.

The present invention relates to the hardening of steel alloys bynitrogenization. It is already known to carry out the nitrogenization atsuch a high temperature that marginal layers are formed which consistprincipally of nitride of iron, Such marginal layers are howeverbrittle, tend to peel oil, and give, therefore no surfaces able forparts which are Sub ected to severe strains. The object of thisinvention it to obviate this disadvantage.

In metallography, in addition to the generally known expressionseutectic and peritectic the expressions eutectoid and peritectoid areusual (see for ex ample, Dr. \V. Guertler, Metallographie, Berlin 1909vol. 1, part 1, pa es 308 and 334). By peritectic is un erstood'thehomogeneous crystalline mass which, at the cooling of alloy belowcertain temperature, inserts itself between the still existin moltenmass and a type of crystal mixe with it, and surrounds the latter. Byperitectoid is understood a structural element corresponding to theperitectic which is formed at a temperature lower than the temperatureof solidification of a liquid alloy, in that at the expense of twoalready existing types of crystals a third type of crystalis formedwhich introduces itself as a separator between the other two andsurrounds oneof them. By transformation is generally understood thebuilding up of a new type of crystal with a simultaneous breaking downof one or more others present. Hence, by temperature of peritectoidaltransformation is to be understood that temperature (varying accordingto the type of alloy), at which the formation of the peritectoid occursupon cooling.

The invention is based on the discovery that steel alloys which haveabsorbed nitrogen, undergo a peritectoidal transformation, which takesplace at a temperature of about 580. If the nitrogenization takes placebelow the peritectoidal transformation temperature, the concentration ofthe Application filed October 26, 1921. Serial Ro. 510,623.

the brittle layers of nitride are formed. In'this case the steelreceives the iron nitride in solid solution to a certain depth and notprincipally as nitride of iron only as in the known process. Themarginal layer formed exhibits a texture which pos- 'sesses thecharacteristic features of the hardening texture of the steel (of themartensite) and therefore acquires a high degree of hardness. Thetransition from the hard marginal layer to the core takes place quitegraduall quently has no tendency to peel off. The hardness diminishesslowly towards the core in proportion as the amount of nitrogencontained decreases. l

The above described process is only suitable for alloyed steels; ordinarcarbon steels do notac uire any great egree of hardness when t ey aresubjected to the action of substances which ive of! nitrogen such asammonia for examp e. The process has been found to be particularlysuitable of application to such ternary and quaternary steel alloyswhich contain aluminium,

and the marginal layer consechromium, manganese or silicon either sep-2,88% Cr is increased by being heated in a current of ammonia at 500from 282 to 471. The hardness of an improved steel containing 0.44%C.,'1.07% Mn and 1.93% Or was increased under the same treatment from298 to 500.

Claims:

1. Process for hardening a steel alloy, consisting in subjecting thealloy to nitrogenization. at a temperature below the temperature ofperitectoidal transformation.

2. Process for hardening a steel alloy containing aluminium, chromium,manganese or silicon in any desired combination, consisting insubjecting the alloy, at a temperature below the temperature oferitectoidal transformation, to the action 0 a substance which givesoflz nitrogen.

The foregoing specification signed at Essen, Germany, th1s 29th day ofSeptember, 1921.

